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nvme-pci: reverse request order in nvme_queue_rqs

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blk_mq_flush_plug_list submits requests in the reverse order that they
were submitted, which leads to a rather suboptimal I/O pattern especially
in rotational devices.  Fix this by rewriting nvme_queue_rqs so that it
always pops the requests from the passed in request list, and then adds
them to the head of a local submit list.  This actually simplifies the
code a bit as it removes the complicated list splicing, at the cost of
extra updates of the rq_next pointer.  As that should be cache hot
anyway it should be an easy price to pay.

Fixes: d62cbcf62f ("nvme: add support for mq_ops->queue_rqs()")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20241113152050.157179-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2024-11-13 16:20:41 +01:00 committed by Jens Axboe
parent e559ee0226
commit beadf00885
1 changed files with 17 additions and 22 deletions
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39
drivers/nvme/host/pci.c
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@ -906,9 +906,10 @@ static blk_status_t nvme_queue_rq(struct blk_mq_hw_ctx *hctx,
static void nvme_submit_cmds(struct nvme_queue *nvmeq, struct request **rqlist)
{
struct request *req;
spin_lock(&nvmeq->sq_lock);
while (!rq_list_empty(*rqlist)) {
struct request *req = rq_list_pop(rqlist);
while ((req = rq_list_pop(rqlist))) {
struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
nvme_sq_copy_cmd(nvmeq, &iod->cmd);
@ -933,31 +934,25 @@ static bool nvme_prep_rq_batch(struct nvme_queue *nvmeq, struct request *req)
static void nvme_queue_rqs(struct request **rqlist)
{
struct request *req, *next, *prev = NULL;
struct request *submit_list = NULL;
struct request *requeue_list = NULL;
struct request **requeue_lastp = &requeue_list;
struct nvme_queue *nvmeq = NULL;
struct request *req;
rq_list_for_each_safe(rqlist, req, next) {
struct nvme_queue *nvmeq = req->mq_hctx->driver_data;
while ((req = rq_list_pop(rqlist))) {
if (nvmeq && nvmeq != req->mq_hctx->driver_data)
nvme_submit_cmds(nvmeq, &submit_list);
nvmeq = req->mq_hctx->driver_data;
if (!nvme_prep_rq_batch(nvmeq, req)) {
/* detach 'req' and add to remainder list */
rq_list_move(rqlist, &requeue_list, req, prev);
req = prev;
if (!req)
continue;
}
if (!next || req->mq_hctx != next->mq_hctx) {
/* detach rest of list, and submit */
req->rq_next = NULL;
nvme_submit_cmds(nvmeq, rqlist);
*rqlist = next;
prev = NULL;
} else
prev = req;
if (nvme_prep_rq_batch(nvmeq, req))
rq_list_add(&submit_list, req); /* reverse order */
else
rq_list_add_tail(&requeue_lastp, req);
}
if (nvmeq)
nvme_submit_cmds(nvmeq, &submit_list);
*rqlist = requeue_list;
}